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  • 1
    Electronic Resource
    Electronic Resource
    Amorphous α-Tricalcium Phosphate: Preparation and Aqueous Setting Reaction (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The mechanical and setting properties of calcium phosphate cements are considerably determined by the pretreatment of the constituents. In this report we show for the first time that prolonged high-energy ball milling of α-tricalcium phosphate (α-TCP) led to mechanically induced phase transformation from the crystalline to the amorphous state. The amorphous material demonstrated a high reactivity such that the time for substantially complete conversion of α-TCP to calcium-deficient hydroxyapatite in 2.5% Na2HPO4 solution decreased from about 20 h (1 h of grinding in ethanol, 85% relative crystallinity) to 4–6 h for a material with a crystallinity of 8% (24 h of grinding). This reactivity could be attributed to an increased thermodynamic and kinetic solubility of the ground materials. Mechanically activated α-TCP cements were produced with compressive strengths of up to 80 MPa and setting times of 5–16 min. The effect of reactant preparation and cement mixing parameters on the physical and chemical properties of mechanically activated α-TCP cement was investigated. By comparing cements of similar porosity and degree of conversion it was demonstrated that apatite specific surface area has a strong influence on cement mechanical performance, which highlights the importance of this previously overlooked parameter in improving strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01126.x
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  • 2
    Electronic Resource
    Electronic Resource
    Cement Formulations in the Calcium Phosphate H2O–H3PO4–H4P2O7 System (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Despite numerous reports of calcium phosphate cement materials, a calcium cement that sets to form a matrix consisting of a pyrophosphate phase has not been reported. The formulation of such a material from the mixture of α-tricalcium phosphate (TCP), β-TCP, or tetracalcium phosphate with a solution containing pyro- and orthophosphoric acid is reported in this study. The effects of liquid and solid compositions on the setting times, compressive strengths and phase compositions of the resultant cements were investigated. It was found that cements could be produced that set to form up to 28 wt% dicalcium pyrophosphate, which appeared by comparison with Rietveld refinement and chemical methods to be entirely amorphous in nature. The solubilities of the different solid components were shown to have a marked effect on the composition of the cements. The strongest cement formulations exhibited compressive strengths comparable with those previously reported in the literature for brushite cements and set within clinically relevant time scales. This class of cement would appear to demonstrate potential as a bone replacement material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00558.x
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanical Activation of Tetracalcium Phosphate (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: It was found that prolonged high-energy ball-milling of Hilgenstokite (tetracalcium phosphate, TTCP) resulted in a decrease in both particle and crystallite size, leading to a mechanical activation of the compound. This mechanically activated material demonstrated a high reactivity such that, in contrast to highly crystalline TTCP, a setting reaction with water to nanocrystalline hydroxyapatite (HA) and Ca(OH)2 could be achieved at 37°C. However, crystalline TTCP is practically unreactive at physiologic temperatures because of the formation of a thin HA layer on the particle surface preventing further reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00311.x
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  • 4
    Electronic Resource
    Electronic Resource
    Stearate Salts as Brushite Bone Cement Setting Retardants (2005)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 284-286 (Apr. 2005), p. 19-22 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This study sought to examine the efficiency of coating cement powder reactants in order to reduce the solubility rate of reactants and thereby increase setting times of cement systems. In this investigation magnesium and sodium stearate salts were used to coat the highly soluble monocalcium phosphate monohydrate (MCPM) powder component of a hydraulic brushite forming calcium phosphate cement system with b-tricalcium phosphate (b-TCP) as other component. The results showed that stearate coating of the MCPM reactant could lead to a 100%increase in setting and working times without affecting compressive strength of the set cement when applied with the appropriate P/L-ratio
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/49/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.284-286.19.pdf
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of Mechanical Mixing and Powder to Liquid Ratio on the Strength and Reliability of a Brushite Bone Cement (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 361-363 (Nov. 2007), p. 307-310 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The effect of mechanical mixing on compressive strength, relative porosity and reliabilityof strength data of a brushite forming cement at different powder to liquid ratios (PLRs) wasinvestigated. Mean compressive strengths were measured, associated reliability (Weibull moduli)and survival probability distributions of the data sets were analysed. Relative porosities weredetermined using helium pycnometry. For low PLR (2.2g/ml), no significant differences incompressive strength were observed for either mechanical or hand mixed samples, althoughreliability of the former was significantly increased. At high PLR (3.4g/ml), mechanically mixedcements exhibited approximately twice the mean compressive strength compared with hand mixing,although Weibull moduli remained statistically similar. At medium PLR (2.8g/ml) strength andreliability of cements were similar and independent of mixing regime. For all PLRs, a significantdecrease in porosity of mechanical- compared with hand-mixed cements was observed. Mechanicalmixing of a brushite cement can provide lower porosity, increased reliability and higher strength
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/56/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.361-363.307.pdf
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  • 6
    Electronic Resource
    Electronic Resource
    Modifying Brushite Cement Degradation Using Calcium Alginate Beads (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 361-363 (Nov. 2007), p. 311-314 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The hydrolysis of brushite in calcium phosphate cements to form hydroxyapatite isknown to result in the long term stability of the material in the body. It has previously beenestablished that this hydrolysis reaction can be influenced by implant volume, media refreshmentrate and media composition. In this study, the effect of macroporosity on the rate of degradation ofthe material is investigated. Macroporosity was incorporated into the material using calciumalginate beads mixed into the cement paste. The inclusion of the calcium alginate beads did notinfluence the degree of conversion of the material and allowed the incorporation of porosity at up tomaximum of 57%. The macroporosity weakened the cement matrix (from 46.5 to 3.2 MPa). Whenaged the brushite in the macroporous cement dissolved completely from the matrix resulting in aweight loss of 60wt% in a period of 28 days. This suggests that the controlled incorporation ofcalcium alginate beads into brushite cements in vivo can be used to control implant degradation rate
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/56/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.361-363.311.pdf
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  • 7
    Electronic Resource
    Electronic Resource
    A Comparison of the Efficacy of Hydoxyapatite Based Cements and Gels as Drug Delivery Matrices (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 361-363 (Nov. 2007), p. 327-330 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: There is a current need for the localized delivery of antibiotics in order to treat implantbased infections. In this study, the efficacy of hydroxyapatite (HA) gels, HA cements, and silicagels in the delivery of vancomycin have been investigated and compared. Vancomycin release wasmonitored at set time points using a UV/VIS spectrophotometer (288 nm). The activity of thevancomycin released from the cements and gels was assessed using an agar diffusion test withStaphylococcus aureus. Vancomycin was released rapidly from both HA matrices, and the silica gelin the first day of the experiment, but the release rate was slowed considerably after 3 days for theHA gels. Following ten days of aging, 70% of the vancomycin remained in the HA gel matrix andthe quantity released from the gel was shown to retain its effectiveness against Staphylococcusaureus
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/56/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.361-363.327.pdf
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  • 8
    Electronic Resource
    Electronic Resource
    The Mechanical Properties and Microstructures of Cement Formed from Pyrophosphoric and Orthophosphoric Acids (2005)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 284-286 (Apr. 2005), p. 125-128 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this study the setting times, compressive strengths and microstructures of cements formed using pyrophosphoric acid solution and b-tricalcium phosphate (β-TCP; Ca3(PO4)2) were compared with those of cement formed using orthophosphoric acid solution and b-TCP. It was found that cement formed using pyrophosphoric acid solution set more slowly than that formed using orthophosphoric acid and could be mixed to a higher powder to liquid ratio, facilitating the production of cement exhibiting compressive strengths, without pre-compaction, as high as 25 MPa. The use of pyrophosphoric acid as opposed to orthophosphoric acid resulted in a marked change in the microstructure of the cement
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/49/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.284-286.125.pdf
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  • 9
    Electronic Resource
    Electronic Resource
    Low Porosity CaHPO〈sub〉4〈/sub〉-2H〈sub〉2〈/sub〉O Cement (2003)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 254-256 (Dec. 2003), p. 205-208 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/47/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.254-256.205.pdf
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  • 10
    Electronic Resource
    Electronic Resource
    Thermodynamic Study of Formation of Amorphous ß-Tricalcium Phosphate for Calcium Phosphate Cements (2003)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 254-256 (Dec. 2003), p. 249-252 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/47/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.254-256.249.pdf
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